1. Field of the Invention
This invention relates to fixation devices for stabilizing two portions of bone, and more particularly to a method and apparatus for the fixation of bone fractures.
2. Description of the Related Art
Repairs of fractures of the distal radius and other small bones of the hand, wrist, and distal forearm often present particular difficulties. Fracture of the distal radius, often referred to by eponyms such as Colles' fractures, Smith's fracture, or Barton's fracture (herein referred to as Colles' fracture), are commonly unstable and may involve complications such as avulsion of the ulnar styloid, tearing of the collateral ulnar ligament, marked displacement of bone fragments from the distal radius or ulna, or derangement of the distal radioulnar joint. Injury to the nearby median nerve by bone spicules may result in sensory and motor paralysis. Persistent compression of the ulnar nerve creates symptoms of carpal tunnel syndrome, which may require operative divension of the volar carpal ligament for relief.
There are two general types of devices which may be used to achieve fixation and, therefore, repair of a Colles' fracture. These devices are generally referred to as external fixation devices and internal fixation devices. External fixation devices are those devices that stabilize a fracture through direct penetration of percutaneous pins into bone and anchorage of the pins to external devices. In contrast, internal fixation devices are those devices that are located completely internal to the body. External fixation devices present several key advantages over internal fixation devices, including simplicity of the operative procedure and minimal disturbance of the bone biology, and decreased risk of deep infection and subsequent nonunion. External fixation is particularly indicated in cases of bone loss to preserve skeletal length.
Techniques of closed reduction and external immobilization using external fixation devices have been advocated for repair of Colles' fractures. Such unstable fractures of the distal radius may be treated with small external fixators with pins implanted in the distal radial epiphysis to allow for early wrist joint mobility. Such external fixation devices are particular advantageous in allowing skeletal distraction and preservation of bone alignment and bone length.
A variety of small external fixators are currently available for application of external fixation principles to small bones, such as the hand and wrist. Brazilian Patent No. 62 00 124 U discloses an external fixation device having percutaneous intramedullary pins and an external clamp with a fixator coupling device for stabilization of distal fractures of the radius, including those defined as Colles' fractures. This device is designed to prevent migration of the frame structure and to promote rotational stability. Because the fixation pins have a smooth surface, however, rotational stability of the pins in relation to the fixator coupling device is not insured. Additionally, because the fixator coupling device has cylindrical attachment grooves to receive the cylindrical ends of the pins to the fixator coupling device, rotational forces are largely unopposed, allowing potential rotation of the pins with resulting instability of the device. Rotational instability is especially likely with this device during the healing process when adjacent muscles and tendons are in use.
Furthermore, the device disclosed in Brazilian Patent No. 62 00 124 U is constructed from a radiodense substance which does not allow easy verification by X-ray of bone alignment during the course of stabilization and healing of the fracture. Additionally, the external clamp of the fixator coupling device is large and bulky, making trauma to the device more likely and subsequent disruption of bone union. The bulkiness of the clamp also makes the desired use of the associated muscles, tendons, and joints during the healing process less likely.